Method for manufacturing aluminum-titanate-based ceramic honeycomb structure

ABSTRACT

A method for manufacturing a ceramic honeycomb structure includes kneading titania particles, alumina particles and a binder such that a raw material paste containing the titania particles, the alumina particles and the binder is prepared, forming a body made of the raw material paste and having the honeycomb structure, and sintering the body having the honeycomb structure such that a ceramic body having the honeycomb structure and made of aluminum titanate is formed. The titania particles are secondary titania particles each comprising primary titania particles aggregated such that the secondary titania particles have a mean volume particle diameter in the range of from 5 μm to 20 μm, and the alumina particles have a mean volume particle diameter in the range of from 2 μm to 5 μm.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of and claims the benefit ofpriority to U.S. Ser. No. 13/887,638, filed May 6, 2013, which is basedupon and claims the benefit of priority to U.S. application Ser. No.61/787,186, filed Mar. 15, 2013. The entire contents of theseapplications are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for manufacturing analuminum-titanate-based ceramic body with a honeycomb structure. Morespecifically, the present invention relates to a method formanufacturing an aluminum-titanate-based ceramic body with a honeycombstructure using a particulate precursor formed of titania particles andalumina particles.

2. Description of Background Art

Japanese Laid-Open Patent Publication No. 2010-189204 describes a methodfor manufacturing a granular aluminum-titanate sintered body, includinga step for extruding and shaping a raw material mixture containing thegranular aluminum-titanate sintered body and a step for sintering thebody obtained by such an extrusion step. The entire contents of JapaneseLaid-Open Patent Publication No. 2010-189204 are incorporated herein byreference.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a method formanufacturing a ceramic body having a honeycomb structure includesbringing titania particles and alumina particles into contact with eachother such that the titania particles and the alumina particles areadhered to each other and form a precursor including particles havingthe titania particles and the alumina particles, combining the precursorwith a binder material such that a raw material paste including theprecursor and the binder material is prepared, forming a body includingthe raw material and having a honeycomb structure, and sintering thebody having the honeycomb structure such that a ceramic body having thehoneycomb structure is formed.

Another aspect of the present invention is a ceramic body having ahoneycomb structure produced by processes including bringing titaniaparticles and alumina particles into contact with each other such thatthe titania particles and the alumina particles are adhered to eachother and form a precursor including particles having the titaniaparticles and the alumina particles, combining the precursor with abinder material such that a raw material paste including the precursorand the binder material is prepared, forming a body including the rawmaterial and having a honeycomb structure, and sintering the body havingthe honeycomb structure such that a ceramic body having the honeycombstructure is formed.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is a perspective view schematically showing an example of aceramic body with a honeycomb structure obtained by the manufacturingmethod according to an embodiment of the present invention;

FIG. 2 is a view showing an end surface of the ceramic body with ahoneycomb structure shown in FIG. 1;

FIG. 3 is a cross-sectional view at line (A-A) of the ceramic body witha honeycomb structure shown in FIG. 1;

FIG. 4 is a flowchart showing an example of the manufacturing methodaccording to an embodiment of the present invention;

FIG. 5 is a view schematically showing an example of a precursor made oftitania particles and alumina particles in an embodiment of the presentinvention; and

FIG. 6 is a view schematically showing another example of a precursormade of titania particles and alumina particles in an embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The embodiments will now be described with reference to the accompanyingdrawings, wherein like reference numerals designate corresponding oridentical elements throughout the various drawings.

FIG. 1 is a perspective view schematically showing an example of aceramic body with a honeycomb structure obtained by the manufacturingmethod according to an embodiment of the present invention.

As shown in FIG. 1, a ceramic honeycomb structure according to anembodiment of the present invention is made of aluminum-titanate-basedceramic body 1 (aluminum-titanate-based sintered body), for example.Ceramic body 1 has two open end surfaces (2A, 2B) and side surface 3.Also, ceramic body 1 has multiple cells made of through-holes 4 andpartitions 5 which section off through-holes 4. Through-holes 4 extendfrom end surface (2A) to end surface (2B) along a longitudinal directionof ceramic body 1 (direction along arrow (a) in FIG. 1), andthrough-holes 4 are sectioned off by partitions 5. In addition, eitherend of a through-hole 4 in a longitudinal direction (a) is sealed bysealant 6, while the other end is left open. Thus, through-hole 4 issealed by sealant 6 only at either end. As shown in FIG. 1, end surfaces(2A, 2B) of ceramic body 1 are in a checkered pattern wherepredetermined portions are alternately sealed. However, end surfaces(2A, 2B) of ceramic body 1 are not limited to such a pattern and may bein any other sealant pattern. The sealant is not limited to any specifictype, and a raw material paste made of titania particles and aluminaparticles or other ceramics may also be used.

The shape of ceramic body 1 may also be an elliptic cylinder, arectangular prism or a polygonal prism instead of a circular cylinder asshown in FIG. 1.

FIG. 2 is a view showing an end surface of ceramic body 1 with ahoneycomb structure shown in FIG. 1.

Through-holes 4 are sectioned off by partitions 5 at end surface (2A) ofceramic body 1 as shown in FIG. 2. Also, some end portions ofthrough-holes 4 are sealed by sealant 6 while others are not sealed bysealant 6 and remain open as shown in FIG. 2. Namely, through-hole 4 issealed by sealant 6 only at either end. Every alternate predeterminedportion at end surface (2A) of ceramic body 1 is sealed so as to form acheckered pattern.

FIG. 3 is a cross-sectional view at line (A-A) of the ceramic body witha honeycomb structure shown in FIG. 1.

As shown in FIG. 3, one end surface (2A) is positioned on the inflowside, and exhaust gas (G) (exhaust gas from a diesel engine, forexample) flows into open through-holes 4, passes through partitions 5which section off through-holes 4, and flows out from otherthrough-holes 4 that are open at the other end surface (2B) on theoutflow side. Therefore, in ceramic body 1 with a honeycomb structureaccording to an embodiment of the present invention, partitions 5 canfunction as a filter to capture particulate matter (PM) or the like, forexample, as a diesel particulate filter (DPF).

Next, a method for manufacturing a ceramic honeycomb structure isdescribed in detail according to an embodiment of the present invention.

FIG. 4 is a flowchart showing an example of the method for manufacturinga honeycomb structure according to an embodiment of the presentinvention.

An example of the method for manufacturing a ceramic honeycomb structureas shown in FIG. 4 includes the following: preconditioning treatmentstep (S1) for forming a precursor by having titania particles andalumina particles come in contact with and adhere to each other;preparation step (S2) for preparing raw material paste by kneading theprecursor and binder ingredients; forming step (S3) for shaping the rawmaterial paste into a honeycomb structure to form a body; drying step(S4) for drying the body shaped from the raw material paste; sealingstep (S5) for sealing either end in a longitudinal direction of athrough-hole of the dried body using a sealant; degreasing step (S6) forremoving organic ingredients from the sealed body; and sintering step(S7) for sintering the body after the organic ingredients are removed sothat a ceramic honeycomb structure is formed.

However, it is an option not to conduct drying step (S4), sealing step(S5) and degreasing step (S6) in the method for manufacturing a ceramichoneycomb structure. Namely, it is an option to conduct preconditioningtreatment step (S1) for forming a precursor by having titania particlesand alumina particles come in contact with and adhere to each other,preparation step (S2) for preparing raw material paste by kneading theprecursor and binder ingredients, and forming step (S3) for shaping theraw material paste into a honeycomb structure to form a body, anddirectly afterward to conduct sintering step (S7) for obtaining aceramic-honeycomb structure by sintering the body obtained by the abovesteps.

In the following, each step is described.

Preconditioning Treatment (S1)

Titania particles and alumina particles are made to come in contact withand adhere to each other to form a precursor (particle contact bodiesformed of titania particles and alumina particles) in thepreconditioning treatment step. Accordingly, precursor particles areobtained where titania particles and alumina particles are homogenouslydistributed and in contact with each other.

In the preconditioning treatment step, a precursor may also be formed byfurther adding a sintering additive to make it come in contact withtitania particles and alumina particles (particle contact bodies formedof titania particles, alumina particles and particles of a sinteringadditive). As for sintering additives, mullite, zircornia, alkalifeldspar, strontium feldspar and the like are listed.

In the present application, titania particles indicate those containingonly titania particles, and alumina particles indicate those containingonly alumina particles. Mullite particles as a sintering additive meanparticles formed with alumina components and silicon dioxide components.Here, titania particles and alumina particles may also containimpurities. As for impurities, for example, silicon (Si), aluminum (Al),iron (Fe), calcium (Ca), magnesium (Mg), potassium (K), sodium (Na) andthe like are listed.

In the present application, “homogenous” or “homogenize” indicates thattitania particles and alumina particles are present evenly based on theamounts of substance (at a molar ratio). It is more preferred that anamount-of-substance ratio of titania to alumina in a precursor be in arange of 40:6060:40, for example. An amount-of-substance ratio heremeans a ratio of the amount of substance of titania to the amount ofsubstance of alumina, not a ratio of the amount of substance of titaniaparticles to the amount of substance of alumina particles. Therefore,when mullite particles or the like are used when forming a precursor, anamount-of-substance ratio of titania to alumina is derived based on thesum (total amount of substance of alumina) of alumina derived fromalumina particles and alumina derived from mullite particles.

To have titania particles and alumina particles come in contact witheach other, the following may be employed, for example: a method inwhich a mixture containing titania particles and alumina particles isspray-dried; a method in which titania particles and alumina particlesare granulated through a rolling motion; a method in which an aqueousdispersion of alumina particles is formed by dispersing aluminaparticles in a dispersion medium such as water, and then titaniaparticles are immersed in the aqueous dispersion of alumina particles;or a method in which a mixture of titania particles and aluminaparticles is slurried and then dried while being mixed.

As for a method in which a mixture containing titania particles andalumina particles is spray-dried, for example, a mixture containingtitania particles and alumina particles is slurried and spray-dried sothat titania particles and alumina particles are homogenized.

In addition, as for another method of spray drying, for example, abinder ingredient to be used in a later-described preparation step isfurther added to the mixture containing titania particles and aluminaparticles at 5%˜10% by mass based on the entire mass of titaniaparticles, and then the mixture is spray-dried.

As for a method in which titania particles and alumina particles aregranulated through a rolling motion, for example, titania particles,alumina particles and water are placed into an oscillating granulatorand then put into a rolling motion to prepare a precursor; titaniaparticles and water are placed into an oscillating granulator and putinto a rolling motion, then alumina particles are added to theoscillating granulator and put into a rolling motion so that a precursoris prepared; and so forth. In such cases, a ratio of 5-10% by mass ofwater based on the entire mass of titania particles is used. Moreover,it is an option to use a binder ingredient (such as methylcellulose)along with water. A ratio of 5-10% by mass of the binder ingredientbased on the entire mass of titania particles may be used.

As for a method in which titania particles are immersed in an aqueousdispersion of alumina particles, for example, alumina particles aredispersed in a dispersion medium such as water to form an aqueousdispersion, titania particles are immersed in the aqueous dispersion ofalumina particles, and then a precursor, in which titania particles andalumina particles are homogenized and in contact with each other, islifted from the aqueous dispersion of alumina particles.

As for a method in which a mixture containing titania particles andalumina particles is slurried and then dried while being mixed, forexample, titania particles and alumina particles are slurried using avolatile solvent or the like to form a homogeneous mixture, which isthen dried while being mixed.

In the preconditioning treatment step, the obtained precursor will notbe sintered directly after the preconditioning treatment step. Uniformparticle diameters of a precursor are thought to be easier to form whilethe precursor and binder ingredients can be kneaded in a short period oftime.

By doing such a preconditioning treatment step, titania particles andalumina particles are more likely to come in contact with each other.Accordingly, precursor 7 is formed, where alumina particles 9 makecontact with titania particle 8 to cover its surface, for example (FIG.5).

FIG. 5 shows a state where titania particle 8 is covered with aluminaparticles 9. That is an example of a precursor. Here, the state of aprecursor is not limited to such a size relationship between titaniaparticles and alumina particles as shown in FIG. 5, and another state,where the size of alumina particles is greater than that of titaniaparticles and the surface of an alumina particle is covered with titaniaparticles, may be employed. In addition, yet another state, where thesize of titania particles is substantially the same as that of aluminaparticles, may also be employed.

Also, when an aggregate of primary particles is used for titaniaparticles, titania particles and alumina particles are even more likelyto come in contact with each other by performing a preconditioningtreatment step as described above. For example, as shown in FIG. 6, aprecursor (7A) is formed, where titania particles (secondary particles)(8B) made of aggregate titania particles (primary particles) (8A) arecovered with alumina particles 9.

In the present application, a “precursor” means a granular materialwhere titania particles and alumina particles make contact with andadhere to each other.

When titania particles, alumina particles and mullite particles makecontact with and adhere to each other, a precursor (a particle contactbody of titania particles, alumina particles and mullite particles) isformed by the same methods described above for having titania particlesand alumina particles come in contact with each other.

To have titania particles, alumina particles and mullite particles comein contact with each other, the following may be employed, for example:a method in which a mixture containing titania particles, aluminaparticles and mullite particles is spray-dried; a method in whichtitania particles, alumina particles and mullite particles aregranulated through a rolling motion; a method in which a mixed aqueousdispersion of alumina particles and mullite particles is formed bydispersing alumina particles and mullite particles in a dispersionmedium such as water, and then titania particles are immersed in themixed aqueous dispersion; or a method in which a mixture of titaniaparticles, alumina particles and mullite particles is slurried and thendried while being mixed.

As for titania particles and alumina particles used in thepreconditioning treatment step, it is an option for titania particlesand alumina particles in a precursor to be combined at anamount-of-substance ratio of titania to alumina in a range of40:60˜60:40, for example. It is also preferable to combine titaniaparticles and alumina particles in a precursor at an amount-of-substanceratio of titania to alumina in a range of 45:55˜55:45, for example.However, if mullite particles are used when preparing a precursor asdescribed above, the value obtained by totaling the alumina derived fromalumina particles and the alumina derived from mullite particlescorresponds to the amount of substance of alumina. Therefore, whenmullite particles are used in the preconditioning treatment step, it ispreferred to combine mullite particles with titania particles andalumina particles in an amount-of-substance ratio of titania to aluminathat is within the above range.

When titania particles and alumina particles are combined in apreconditioning treatment step, their weight ratio is, for example, in arange of 35:65˜55:45, more preferably, 40:60˜50:50. The amount ofunreacted titania or alumina remaining after sintering is reduced ifcombined within such a ratio.

Particle diameters of titania particles and alumina particles are notlimited specifically. For example, when particle diameters of titaniaparticles and alumina particles are compared, it is an option to employany of the following: the diameter of titania particles is greater thanthat of alumina particles; the diameter of titania particles is smallerthan that of alumina particles; or the diameter of titania particles issubstantially the same as that of alumina particles.

In a preconditioning treatment step, when alumina particles are usedwith titania particles having a particle diameter greater than that ofalumina particles, it is referred to as a “first embodiment” in thefollowing. In addition, when alumina particles are used with titaniaparticles having a particle diameter smaller than that of aluminaparticles, it is referred to as a “second embodiment” and described inthe following. Moreover, when alumina particles are used with titaniaparticles having a particle diameter substantially the same as that ofalumina particles, it is referred to as a “third embodiment” anddescribed in the following.

In the first embodiment, when alumina particles are combined withtitania particles having a particle diameter greater than aluminaparticles, that makes it easier to form a precursor where multiplealumina particles are in contact with the surface of a titania particle.

As for the particle diameter of titania particles in the firstembodiment, the mean volume particle diameter is 5 μm˜20 μm, forexample. Also, particles with a mean volume particle diameter of 8 μm˜18μm or the like may be used. Here, it is an option to use primaryparticles of titania particles or secondary particles which areaggregate primary particles, or to use a combination thereof.

In the present application, mean volume particle diameters are measuredusing a laser diffraction particle size distribution analyzer (BeckmanCoulter Inc.).

As for the particle diameter of alumina particles in the firstembodiment, the mean volume particle diameter is 2 μm˜5 μm, for example.

In the present application, the type of alumina particles is not limitedspecifically. For example, α-alumina particles, γ-alumina particles, acombination of α-alumina particles and γ-alumina particles, or the likemay be used. In addition, alumina particles may be primary particles,secondary particles that are aggregate primary particles, or acombination thereof.

In the first embodiment, the ratio of particle diameters of titaniaparticles and alumina particles is not limited specifically, and it maybe in a range of 10:1˜10:3, for example.

A second embodiment is described in the following, using aluminaparticles and titania particles having a smaller particle diameter thanalumina particles.

To have titania particles and alumina particles come in contact witheach other in the second embodiment, the following may be employed, forexample: a method in which a mixture containing titania particles andalumina particles is spray-dried; a method in which titania particlesand alumina particles are granulated through a rolling motion; a methodin which an aqueous dispersion of alumina particles is formed bydispersing alumina particles in a dispersion medium such as water andthen titania particles are immersed in the aqueous dispersion of aluminaparticles; or a method in which a mixture of titania particles andalumina particles is slurried, and is dried while being mixed. As for amethod for granulating titania particles and alumina particles through arolling motion, a precursor may also be prepared when alumina particlesand water are placed into an oscillating granulator, put into a rollingmotion, and then titania particles are added into the oscillatinggranulator and put into a rolling motion.

As for the particle diameter of titania particles in the secondembodiment, the mean volume particle diameter is 0.1 μm˜0.8 μm or 0.2μm˜0.5 μm, for example.

As for the particle diameter of alumina particles in the secondembodiment, the mean volume particle diameter is 2 μm˜5 μm, for example.

In the second embodiment, it is easier to form a precursor where titaniaparticles are in contact with the surface of an alumina particle.

In the second embodiment, the ratio of particle diameters of titaniaparticles and alumina particles is not limited specifically, and it maybe in a range of 1:4˜1:10, for example.

Furthermore, a third embodiment is described, using titania particlesand alumina particles having substantially the same particle diametersas each other in a preconditioning treatment step.

To have titania particles and alumina particles come in contact witheach other in the second embodiment, the following may be employed, forexample: a method in which a mixture containing titania particles andalumina particles is spray-dried; a method in which titania particlesand alumina particles are granulated through a rolling motion; a methodin which an aqueous dispersion of alumina particles is formed bydispersing alumina particles in a dispersion medium such as water andthen titania particles are immersed in the aqueous dispersion of aluminaparticles; a method in which an aqueous dispersion of titania particlesis formed by dispersing titania particles in a dispersion medium such aswater and then alumina particles are immersed in the aqueous dispersionof titania particles; or a method in which a mixture of titaniaparticles and alumina particles is slurried, and is dried while beingmixed.

As for the particle diameter of titania particles in the thirdembodiment, the mean volume particle diameter is 1 μm˜5 μm or 1 μm˜3 μm,for example.

As for the particle diameter of alumina particles in the thirdembodiment, the mean volume particle diameter is 2 μm˜5 μm, for example.

In the third embodiment, titania particles with a particle diametersubstantially the same as that of alumina particles are combined withalumina particles. That makes it easier to form a mixture of a precursorwhere multiple alumina particles are in contact with the surface of atitania particle, a precursor where multiple titania particles are incontact with the surface of an alumina particle, and the like.

In the third embodiment, the ratio of particle diameters of titaniaparticles and alumina particles is not limited specifically, and it maybe in a range of 1.0:0.3˜1.0:4.0, for example.

As for the particle diameter of mullite particles to be used in additionto titania particles and alumina particles when needed, the mean volumeparticle diameter is 0.1 μm˜45 μm, for example. Alternatively, a meanvolume particle diameter of 0.1 μm˜20 μm, 0.5 μm˜10 μm and so forth, forexample, may also be used. When a body is sintered and aluminum titanateis formed, unreacted aluminum and silicon contained in mullite particlesare thought to melt and work as a binder which fills spaces in aluminumtitanate.

The mullite particles may be primary particles, secondary particleswhich are aggregate primary particles, or a combination thereof.

It is an option for the powder of titania particles (titania powder)containing titania particles used for a precursor to include impuritiessuch as silicon (Si), aluminum (Al), iron (Fe), calcium (Ca), magnesium(Mg), potassium (K) and sodium (Na). In the present application,“titania particle powder” means bulk (material, raw material) of titaniaparticles to be used in a method for manufacturing a ceramic honeycombstructure. Here, impurities in titania powder may be such that arecontained inevitably during a process of manufacturing titania, or maybe such that are mixed into titania powder separately. In addition toimpurities that make solid solutions with titania particles, otherimpurities that are present outside titania particles of titania powdermay also be included.

It is thought that those impurities contribute to suppressing aluminumtitanate, which is manufactured using a precursor where titaniaparticles and alumina particles are in contact with and adhere to eachother, from being decomposed into titania and alumina in a hightemperature range, or to improving the mechanical strength of aluminumtitanate.

The amount of impurities is adjusted by controlling the amount ofimpurities contained in raw titania material such as Ti(OH)₄ (titaniapowder) or the like or by cleansing titania compounds by using acids,alkalis or the like.

The amount of iron in titania powder is preferred to be at a weightratio of 200 ppm˜1000 ppm in the titania powder in terms of Fe₂O₃. Whenthe amount of iron in titania powder is in the above range, it isthought that aluminum titanate formed when part of Al³⁺ is displaced byFe²⁺ is suppressed from being decomposed into titania and alumina in ahigh temperature range.

The amount of silicon contained in titania powder is preferred to be 0.1wt. %˜1.0 wt. % of the titania powder in terms of SiO₂. When the amountof silicon in titania powder is in the above range, it is thought thataluminum titanate formed when part of Al³⁺ is displaced by Si⁴⁺ issuppressed from being decomposed into titania and alumina in a hightemperature range.

No magnesium is preferred to be contained in titania powder. Whencontained, the amount of magnesium in titania powder is preferred to beat a weight ratio of 500 ppm or lower in the titania powder in terms ofMgO. Since MgO tends to absorb water, if MgO exists at particleboundaries among aluminum titanate particles, it is thought MgO maycause cracking due to expansion from moisture absorption. Thus, theamount of magnesium in titanate powder is preferred to be within theabove range. Alternatively, it is preferred that no magnesium, orsubstantially no magnesium (at or below the detection limit), becontained in titania powder.

The amount of potassium in titania powder is preferred to be at a weightratio of 100 ppm˜600 ppm in the titania powder in terms of K₂O. Inaddition, the amount of sodium in titania powder is preferred to be at aweight ratio of 200 ppm˜1000 ppm in the titania powder in terms of Na₂O.It is thought that K₂O and Na₂O work as sintering additives for sinterbonding aluminum titanate particles to each other so as to suppresscracking at particle boundaries among aluminum titanate particles. Thus,the amounts of potassium and sodium in titania powder are preferred tobe in the above ranges.

Preparation of Raw Material Paste (S2)

In a raw material paste preparation step, raw material paste is preparedby kneading binder ingredients and a precursor formed to have aluminaparticles and titania particles come in contact homogeneously.

A method for kneading a precursor and binder ingredients is not limitedspecifically, and a mixer, a kneader, a media mixing mill (attritor), apressure kneader (muller) or the like may be used for kneading.

As for a binder ingredient, the following are listed: celluloses such asmethylcellulose, carboxymethyl cellulose and sodium carboxymethylcellulose; alcohols such as polyvinyl alcohol; salts such aslignosulfonate; waxes such as paraffin wax and microcrystalline wax; andthermoplastic resins such as EVA, polyethylene, liquid-crystal polymerand engineering plastics.

The amount of a binder ingredient to be added is, for example, 0.1%˜20%by mass based on 100% by mass of a precursor. It may be 1%˜15% by mass,for example.

To prepare raw material paste, other ingredients may be added to aprecursor and binder ingredients.

As for other ingredients, pore-forming agents, lubricants, plasticizers,dispersing agents, solvents and the like are listed.

For pore-forming agents, the following are listed: carbon materials suchas graphite; resins such as polyethylene, polypropylene andpolymethylmethacrylate; plant-based materials such as starch, nutshells, walnut shells and corn; ice; dry ice; and the like.

The amount of a pore-forming agent to be added is 0.1%˜30% by mass basedon 100% by mass of a precursor. It may be 1%˜20% by mass, for example.

For lubricants and plasticizers, the following are listed, for example:alcohols such as glycerin; higher fatty acids such as caprylic acid,lauric acid, palmitic acid, alginic acid, oleic acid and stearic acid;and metal stearate such as aluminum stearate.

The amount of a lubricant or plasticizer to be added is 0.01%˜5% by massbased on 100% by mass of a precursor. It may be 0.1%˜1% by mass.

As for dispersing agents, the following, for example, are listed:inorganic acids such as nitric acid, hydrochloric acid and sulfuricacid; organic acids such as oxalic acid, citric acid, acetic acid, malicacid and lactic acid; alcohols such as methanol, ethanol and propanol;surfactants such as ammonium polycarboxylate and polyoxyalkylene alkylether; and so forth.

The amount of a dispersing agent to be added is 0.01%˜10% by mass basedon 100% by mass of a precursor. It may be 0.05%˜2% by mass.

As for solvents, the following are listed, for example: alcohols such asmethanol, ethanol, butanol and propanol; glycols such as propyleneglycol, polypropylene glycol and ethylene glycol; water; and the like.

The amount of a solvent to be used is 0.1%˜50% by mass. It may be10%˜40% by mass.

Forming of Honeycomb Structural Body (S3)

In a honeycomb structural body forming step, a body is formed by shapingthe raw material paste into a honeycomb structure.

Forming raw material paste into a shape is not limited specifically, andextrusion methods using a honeycomb die or the like may be employed.

Drying (S4)

In a drying step, a body shaped from the raw material paste is dried.

Dryers for a drying step are not limited to any specific type, and thefollowing are listed: microwave dryers, hot-air dryers, dielectricheating dryers, reduced-pressure dryers, vacuum dryers, freeze dryersand the like.

The duration and temperature for drying are set appropriately accordingto the volume or the like of a honeycomb body.

Sealing of Through-holes (S5)

In a through-hole sealing step, either end of a through-hole in thedried body in their longitudinal direction is sealed using a sealant.

Application of a sealant to a honeycomb body is not limitedspecifically. There are methods such as immersing an end surface of abody into sealant slurry, injecting a sealant into a through-hole froman end surface using an injector, and the like.

As for a sealant, it is not limited to any specific type. For example,raw material paste made of titania particles and alumina particles, ormade of other ceramic, may be used.

Sealant slurry is prepared by adding a binder ingredient, water or thelike to titania particles and alumina particles, for example. Theviscosity of sealant slurry is adjusted properly according to the typeand the like of the sealant.

It is an option to conduct a sealing step after a sintering step.

Degreasing of Honeycomb Structural Body (S6)

In a degreasing step, organic ingredients are removed from the sealedbody.

Conditions for removing organic ingredients from the sealed honeycombbody are not limited specifically, and may be selected according to thetype and amount of organic ingredients contained in the honeycomb body.For example, degreasing is conducted at 150° C.˜800° C. for two hours.

Sintering of Honeycomb Structural Body (S7)

In a sintering step, a ceramic honeycomb structure is obtained bysintering a body from which organic ingredients have been removed.

Sintering is not limited to any specific method and is conducted using asintering furnace such as an electric tube furnace, electric boxfurnace, tunnel kiln, far infrared furnace, microwave heater, shaftkiln, reverberatory furnace, rotary-hearth furnace or roller-hearthfurnace.

As for sintering methods, a body may be sintered batch by batch orcontinuously. Alternatively, a body may be settled or circulated whilebeing sintered.

The sintering temperature is 1350° C. or higher, for example, and it maybe set at 1400° C. or higher. In addition, the sintering temperature is1650° C. or lower, for example, and it may be set at 1550° C. or lower.

The programmed rate of the sintering temperature is not limitedspecifically, and it may be set at 1° C./hour˜500° C./hour, for example.

Sintering a honeycomb body is conducted under oxygen atmosphere such asatmospheric air, for example.

The duration for sintering a honeycomb body differs depending on theamount of raw material paste, the type of sintering furnace, thesintering temperature, the sintering atmosphere and the like. It may beset for 10 minutes˜24 hours, for example.

Ceramic Body Having Honeycomb Structure

A ceramic honeycomb structure according to an embodiment of the presentinvention is obtained by a manufacturing method that includes thefollowing: a preconditioning treatment step for forming a precursor byhaving titania particles and alumina particles come in contact with eachother; a preparation step for preparing raw material paste by kneadingthe precursor and binder ingredients; a forming step for shaping the rawmaterial paste into a honeycomb structure to form a body; and asintering step for sintering the body to obtain a ceramic body with ahoneycomb structure.

When an element analysis is performed on the obtained ceramic body usinga scanning electron microscope (S-4800, Hitachi, Ltd.) and an energydispersive X-ray spectrometer (EMAX Energy EX-250, Horiba, Ltd.), theratio (weight ratio) of titania and alumina in a ceramic body ispreferred to be in a range of 7:10˜4:10, more preferably in a range of6:10˜5:10.

In addition, it is preferred that titania be contained at 15 wt. %˜50wt.% and alumina at 45 wt. %˜70 wt. % of the entire weight of theobtained ceramic body; more preferably, titania at 22 wt. %˜40 wt.% andalumina at 55 wt. %˜65 wt. %. Furthermore, it is an option for silica tobe contained at 1 wt. %˜20 wt. % or 3 wt. %˜15 wt. % of the entireweight of the obtained ceramic body.

Partitions of a ceramic body with a honeycomb structure can function asa filter to capture particulate matter (PM).

Therefore, a ceramic honeycomb structure can function, for example, as adiesel particulate filter (DPF) or the like.

EXAMPLES

Examples according to the present invention are further described indetail. However, the present invention is not limited to such examples.

Example 1

Eight parts by weight of titania particles with a mean volume particlediameter of 12 μm (brand name TiO₂ 3020 (registered mark), KronosIncorporated), 10 parts by weight of alumina particles with a meanvolume particle diameter of 3 μm (brand name Al₂O₃ RMA (registeredmark), Alcan Inc.), and 40 parts by weight of water are placed into aspray dryer (G8210-A, Yamato Scientific Co., Ltd.) and spray dried toform a precursor.

The precursor, 6 parts by weight of alumina particles, 3 parts by weightof silicon dioxide, 20 parts by weight of pore-forming graphite (brandname A625, Asbury Graphite Mills, Inc.) and 4.5 parts by weight ofmethyl cellulose (brand name METOLOSE 60SH, Shin-Etsu Chemical Co.,Ltd.) are placed into a kneader (brand name Mix Muller, Shinto KogyoK.K.) and kneaded to prepare raw material paste.

The raw material paste is extruded through a honeycomb die to form abody with a honeycomb structure having approximately 300 cpsi(approximately 46.5 cell/cm²) with a partition thickness ofapproximately 0.010 inch (approximately 0.25 mm). The raw material pasteis shaped into a body with a length of 150 mm and a diameter of 143.8mm.

Then, a body is cut to a desired length and dried for 20 minutes usingboth microwave (2.45 GHz, 20 kW) and hot air (140° C., air speed of 1m/s).

Next, sealant slurry is prepared from the same raw material paste asused for the honeycomb body.

Masking films are put on both end surfaces of the dried body. Then, themasking films are bored into a checkered pattern so that the ceramicbody with a honeycomb structure obtained after sintering is sealed incheckered patterns which are complementary on one end surface and on theother end surface of the ceramic body. Accordingly, a masked body isformed. As for masking film, a tape with an adhesive layer (adhesiveforce of 5.3 N/cm) made by forming acrylic adhesive on a polyester baseis used.

The portion from an end sealed with masking film to a point 5 mm upwardin a longitudinal direction of a dried body is immersed into sealantslurry. Then, the body is lifted from the sealant slurry. In the samemanner, the other end of the body in a longitudinal direction is alsoimmersed into the sealant slurry and lifted from the sealant slurry.Accordingly, a sealed body is obtained.

Under atmospheric air, the sealed body is heated from room temperatureto 200° C. at a programmed rate of 40° C./hour; when the temperature hasreached 200° C., it is heated to 300° C. at a programmed rate of 10°C./hour; when the temperature has reached 300° C., it is heated to 450°C. at a programmed rate of 40° C./hour; the temperature is kept at 450°C. for 5 hours to degrease the body; and it is heated at a programmedrate of 500° C./hour to 1450° C., where it is kept for 5 hours to sinterthe body. Accordingly, a ceramic body with a honeycomb structure isobtained.

An element analysis is performed on the obtained ceramic body using ascanning electron microscope (S-4800, Hitachi, Ltd.) and an energydispersive X-ray spectrometer (EMAX Energy EX-250, Horiba, Ltd.). As aresult, the ratio (weight ratio) of titania and alumina in the ceramicbody is found in a range of 6:10˜5:10.

Example 2

Eight parts by weight of titania particles with a mean volume particlediameter of 12 μm (brand name TiO₂ 3020 (registered mark), KronosIncorporated), 9 parts by weight of alumina particles with a mean volumeparticle diameter of 3 μm (brand name Al₂O₃ RMA (registered mark), AlcanInc.), 2 parts by weight of mullite particles with a mean volumeparticle diameter of 0.7 μm (brand name KM102, KCM Corporation Co.,Ltd.), and 40 parts by weight of water are placed into a spray dryer(G8210-A, Yamato Scientific Co., Ltd.) and spray dried. Accordingly, aprecursor is produced.

The precursor, 6 parts by weight of alumina particles, 20 parts byweight of pore-forming graphite (brand name A625, Asbury Graphite Mills,Inc.) and 4.5 parts by weight of methyl cellulose (brand name METOLOSE60SH, Shin-Etsu Chemical Co., Ltd.) are placed into a kneader (brandname Mix Muller, Shinto Kogyo K.K.) and kneaded to prepare raw materialpaste.

The same as in Example 1, a body shaped from the raw material paste iscut to a desired length, dried, sealed, degreased and sintered.Accordingly, a ceramic body with a honeycomb structure is obtained.

Example 3

Eight parts by weight of titania particles with a mean volume particlediameter of 1 μm˜2 μm (brand name TI-0059, Soekawa Chemical Co., Ltd.),10 parts by weight of α-alumina particles with a mean volume particlediameter of 2 μm˜3 μm (brand name AL-0123, Soekawa Chemical Co., Ltd.),and 40 parts by weight of water are placed into a spray dryer (G8210-A,Yamato Scientific Co., Ltd.) and spray dried. Accordingly, a precursoris produced.

The precursor, 6 parts by weight of α-alumina particles, 20 parts byweight of pore-forming graphite (brand name A625, Asbury Graphite Mills,Inc.), and 4.5 parts by weight of methyl cellulose (brand name METOLOSE60SH, Shin-Etsu Chemical Co., Ltd.) are placed into a kneader (brandname Mix Muller, Shinto Kogyo K.K.) and kneaded to prepare raw materialpaste.

The same as in Example 1, a body shaped from the raw material paste iscut to a desired length, dried, sealed, degreased and sintered.Accordingly, a ceramic body with a honeycomb structure is thought to beobtained based on the accumulated knowledge of the inventor.

Example 4

Eight parts by weight of titania particles with a mean volume particlediameter of 0.3 μm˜0.5 μm (brand name TI-0068, Soekawa Chemical Co.,Ltd.), 10 parts by weight of γ-alumina particles with a mean volumeparticle diameter of 2 μm˜3 μm (brand name AL-0147, Soekawa ChemicalCo., Ltd.), and 40 parts by weight of water are placed into a spraydryer (G8210-A, Yamato Scientific Co., Ltd.) and spray dried.Accordingly, a precursor is produced.

The precursor, 6 parts by weight of γ-alumina particles, 20 parts byweight of pore-forming graphite (brand name A625, Asbury Graphite Mills,Inc.), and 4.5 parts by weight of methyl cellulose (brand name METOLOSE60SH, Shin-Etsu Chemical Co., Ltd.) are placed into a kneader (brandname Mix Muller, Shinto Kogyo K.K.) and kneaded to prepare raw materialpaste.

The same as in Example 1, a body shaped from the raw material paste iscut to a desired length, dried, sealed, degreased and sintered.Accordingly, a ceramic body with a honeycomb structure is thought to beobtained based on the accumulated knowledge of the inventor.

Evaluation

The components that form ceramic bodies obtained in Examples 1 and 2 areanalyzed using an X-ray diffractometer (D8 DISCOVER, Bruker AXS GmbH).The more the amount of detected alumina and titania, and the less theamount of aluminum titanate, it is found that the ratios of remainingunreacted alumina and titania in the raw material are high and thataluminum titanate corresponding to such ratios is not produced.

As a result of the analysis, the ratio of remaining alumina in theceramic body obtained in Examples 1 and 2 is approximately 6%˜9%. Theratio of alumina in ceramic bodies obtained in Examples 3 and 4 isthought to be approximately the same.

Distribution of pores and the size of pores in partitions are constantin the ceramic bodies obtained in Examples 1 and 2.

A method for manufacturing a ceramic honeycomb structure according to anembodiment of the present invention includes the following: apreconditioning treatment step for forming a precursor by having titaniaparticles and alumina particles come in contact with and adhere to eachother; a preparation step for preparing raw material paste by kneadingthe precursor and binder ingredients; a forming step for shaping thematerial paste into a honeycomb structure to form a body; and asintering step for sintering the body to obtain a ceramic body with ahoneycomb structure.

Another embodiment of the present invention is a ceramic body obtainedby a method for manufacturing a ceramic honeycomb structure whichincludes the following: a preconditioning treatment step for forming aprecursor by having titania particles and alumina particles come incontact with and adhere to each other; a preparation step for preparingraw material paste by kneading the precursor and binder ingredients; aforming step for shaping the raw material paste into a honeycombstructure to form a body; and a sintering step for sintering the body toobtain a ceramic body with a honeycomb structure.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

What is claimed is:
 1. A method for manufacturing a ceramic honeycombstructure, comprising: kneading titania particles, alumina particles anda binder such that a raw material paste comprising the titaniaparticles, the alumina particles and the binder is prepared; forming abody comprising the raw material paste and having the honeycombstructure; and sintering the body having the honeycomb structure suchthat a ceramic body having the honeycomb structure and comprisingaluminum titanate is formed, wherein the titania particles are secondarytitania particles each comprising primary titania particles aggregatedsuch that the secondary titania particles have a mean volume particlediameter in a range of from 5 μm to 20 μm, and the alumina particleshave a mean volume particle diameter in a range of from 2 μm to 5 μm. 2.The method for manufacturing a ceramic honeycomb structure according toclaim 1, further comprising forming a precursor comprising particlescomprising the titania particles and the alumina particles, wherein theforming of the precursor comprises bringing the titania particles andthe alumina particles into contact with each other such that the titaniaparticles and the alumina particles are adhered to each other and formthe precursor comprising the particles comprising the titania particlesand the alumina particles, and the kneading comprises kneading thebinder ingredient and the particles of the precursor comprising thetitania particles and the alumina particles.
 3. The method formanufacturing a ceramic honeycomb structure according to claim 2,wherein the forming of the precursor includes spray-drying the aluminaparticles onto the titania particles.
 4. The method for manufacturing aceramic honeycomb structure according to claim 1, wherein the kneadingincludes combining mullite particles, the binder, the titania particlesand the alumina particles such that a raw material paste comprising themullite particles, the titania particles, the alumina particles and thebinder is prepared.
 5. The method for manufacturing a ceramic honeycombstructure according to claim 1, wherein the kneading includes combininga pore-forming agent, the binder, the titania particles and the aluminaparticles such that a raw material paste comprising the pore-formingagent, the titania particles, the alumina particles and the binder isprepared.
 6. The method for manufacturing a ceramic honeycomb structureaccording to claim 5, wherein the pore-forming agent is at least onematerial selected from the group consisting of a graphite material, apolyethylene material, a polypropylene material, apolymethylmethacrylate material, a starch material, a nut shellmaterial, a walnut shell material, a corn material, an ice material, anda dry ice material.
 7. The method for manufacturing a ceramic honeycombstructure according to claim 1, wherein the kneading includes combininga sintering additive, the binder, the titania particles and the aluminaparticles such that a raw material paste comprising the sinteringadditive, the titania particles, the alumina particles and the binder isprepared.
 8. The method for manufacturing a ceramic honeycomb structureaccording to claim 1, wherein the kneading includes combining asintering additive comprising mullite particles, the binder, the titaniaparticles and the alumina particles such that a raw material pastecomprising the sintering additive, the titania particles, the aluminaparticles and the binder is prepared.
 9. The method for manufacturing aceramic honeycomb structure according to claim 5, wherein thepore-forming agent is added in an amount in a range of 0.1% to 30% bymass based on 100% by mass of the precursor.
 10. The method formanufacturing a ceramic honeycomb structure according to claim 1,wherein the titania particles and the alumina particles have a ratio ofa particle diameter of the titania particles to a particle diameter ofthe alumina particles in a range of from 10:1 to 10:3.
 11. The methodfor manufacturing a ceramic honeycomb structure according to claim 1,wherein the binder material includes at least one binder selected fromthe group consisting of a cellulose, an alcohol, a salt, a wax and athermoplastic resin.
 12. The method for manufacturing a ceramichoneycomb structure according to claim 2, wherein the kneading includescombining mullite particles, the binder and the precursor such that araw material paste comprising the mullite particles, the precursor andthe binder is prepared.
 13. The method for manufacturing a ceramichoneycomb structure according to claim 2, wherein the kneading includescombining a pore-forming agent, the binder and the precursor such that araw material paste comprising the pore-forming agent, the precursor andthe binder is prepared.
 14. The method for manufacturing a ceramichoneycomb structure according to claim 13, wherein the pore-formingagent is at least one material selected from the group consisting of agraphite material, a polyethylene material, a polypropylene material, apolymethylmethacrylate material, a starch material, a nut shellmaterial, a walnut shell material, a corn material, an ice material, anda dry ice material.
 15. The method for manufacturing a ceramic honeycombstructure according to claim 2, wherein the kneading includes combininga sintering additive, the binder and the precursor such that a rawmaterial paste comprising the sintering additive, the precursor and thebinder is prepared.
 16. The method for manufacturing a ceramic honeycombstructure according to claim 2, wherein the kneading includes combininga sintering additive comprising mullite particles, the binder and theprecursor such that a raw material paste comprising the sinteringadditive, the precursor and the binder is prepared.
 17. The method formanufacturing a ceramic honeycomb structure according to claim 13,wherein the pore-forming agent is added in an amount in a range of 0.1%to 30% by mass based on 100% by mass of the precursor.
 18. The methodfor manufacturing a ceramic honeycomb structure according to claim 2,wherein the titania particles and the alumina particles have a ratio ofa particle diameter of the titania particles to a particle diameter ofthe alumina particles in a range of from 10:1 to 10:3.
 19. The methodfor manufacturing a ceramic honeycomb structure according to claim 2,wherein the binder material includes at least one binder selected fromthe group consisting of a cellulose, an alcohol, a salt, a wax and athermoplastic resin.
 20. A ceramic honeycomb structural body produced bythe method for manufacturing a ceramic honeycomb structure according toclaim 1.